Structural characterization of newly-developed Al79Ni5Fe5Y11 and Al79Ni11Fe5Y5 alloys with amorphous matrixes

The low glass-forming ability of aluminium-based metallic glasses significantly limits their development and preparation. This paper updates the current state of knowledge by presenting the results of structural studies of two newly-developed Al79Ni5Fe5Y11 and Al79Ni11Fe5Y5 alloys with a reduced aluminium content (< 80 at.%). The alloys were produced by conventional casting (ingots) and melt-spinning (ribbons). Structural characterization was carried out for bulk ingots first, and then for the melt-spun ribbons. The ingots possessed a multiphase crystalline structure, as confirmed by X-ray diffraction and scanning electron microscopy observations. The amorphous structure of the melt-spun ribbons was determined by X-ray diffraction and transmission electron microscopy. SEM observations and EDX element maps of the cross-section of melt-spun ribbons indicated a homogeneous elemental composition. Neutron diffraction revealed the presence of nanocrystals in the amorphous matrix of the melt-spun ribbons. DSC data of the melt-spun ribbons showed exothermic events corresponding to the first crystallization at temperatures of 408 °C and 387 °C for Al79Ni5Fe5Y11 and Al79Ni11Fe5Y5, respectively.


Materials and methods
Two newly-developed Al 79 Ni 5 Fe 5 Y 11 and Al 79 Ni 11 Fe 5 Y 5 alloys with a reduced aluminium content (< 80 at.%) were studied.Ingots of Al, Ni, Fe, and Y elements with a purity of 99.99% were melted in an induction furnace under a protective argon atmosphere in cylindrical corundum crucibles and then slowly cooled.The dimensions of the ingots were 50 mm high and 30 mm in diameter.The ingots produced were remelted and cast into ribbons by rapidly cooling from the liquid state by melt-spinning using a Bühler Melt Spinner SC station.The linear speed of the copper wheel with a diameter of 200 mm via the melt-spinning method was 30 m/s, which corresponds to a rotational speed of approximately 2865 rpm.The ribbon casting temperature was 1400 °C for Al 79 Ni 5 Fe 5 Y 11 alloy and 1200 °C for Al 79 Ni 11 Fe 5 Y 5 alloy.The melt-spun ribbons were approximately 50 μm thick and 10 mm wide.
X-ray diffraction (XRD) patterns were recorded using a Mini Flex 600 equipped with a copper tube Cu Kα (λ = 0.154 nm) as the X-ray radiation source and a D/TEX strip detector.The XRD patterns were collected in the Bragg-Brentano geometry.Samples in the form of ribbons were powdered for XRD measurements.
Neutron diffraction studies of alloys in the form of melt-spun alloys were performed on the MTEST neutron powder diffractometer at the Budapest Neutron Center.The powdered ribbons were measured in vanadium cans with a diameter of 6 mm.The Cu (111) monochromator selected neutrons with a wavelength of λ = 0.145 nm.
Observations of the microstructures were made using a Cs-corrected transmission electron microscope S/ TEM Titan 80-300 from FEI Company.High-resolution transmission electron microscopy (HRTEM) imaging was also used.The diffraction patterns were obtained with both selected area diffraction (SAED) and Fourier transformations from HRTEM images.The melt-spun samples in the form of circles with a diameter of 3 mm were processed by a precise ion polishing system (Gatan 691).
The microstructures of alloy ingots were characterized by scanning electron microscopy (EVO MA10, Carl Zeiss) using the backscattered electron (BSE) mode.The cross-sections of melt-spun ribbons were observed using the secondary electron (SE) mode (Supra 35, Carl Zeiss).The maps of chemical elements were obtained by using energy-dispersive X-ray spectroscopy (EDX). 57Fe Mössbauer transmission spectra were recorded at room temperature with an MS96 Mössbauer spectrometer and a linearly-arranged 57 Co:Rh source.Numerical analysis of the Mössbauer spectra was performed using the WMOSS program.
The crystallization mechanisms of the studied alloys in the form of ribbons were described using differential scanning calorimetry (DSC).Two temperature ranges were used: from 200 to 1000 °C by using a thermal analyzer SDT Q600 (Al 2 O 3 /Al 2 O 3 ) and from 200 to 700 °C by a 910 model (DuPont Company (Pt/Pt)).

Ethical approval
This article does not contain any studies with human participants or animals performed by any of the authors.

Results and discussion
To identify the structure of Al 79 Ni 5 Fe 5 Y 11 and Al 79 Ni 11 Fe 5 Y 5 alloys in the form of slowly-cooled ingots, X-ray diffraction was carried out.Figure 1  The X-ray phase analysis of the Al 85 Ni 5 Fe 5 Y 5 alloy, with a similar chemical composition to the studied alloys, is presented in ref. 19 .Similarly to the studied alloys, this alloy contained α-Al.In addition, Al 23 Ni 6 Y 4 and Al 10 Fe 2 Y phases were identified in the Al 79 Ni 5 Fe 5 Y 11 alloy.In ref. 20 , the authors proved that during annealing of the Al 86 Ni 8 Y 6 alloy with an amorphous structure, the Al 23 Ni 6 Y 4 phase crystallized first, followed by the α-Al phase due to the local depletion of nickel and yttrium in the metallic liquid.However, according to the research results described in ref. 21 The microstructures of Al-Zr-Ni-Fe-Y alloys in the form of ingots are presented in ref. 22 , in which the Al 3 Y phase was present in the form of small platelets.However, the Al 3 Y phase in the SEM microstructures of Al-Y-Fe master alloys was observed in the form of longitudinal, regular precipitates in ref. 23 .The Al 10 Fe 2 Y phase in the Al 88 Y 8−x Fe 4+x alloys (x = 0, 1, 2 at.%) formed a dendritic structure, while the α-Al phase was the matrix, which was characterized by the darkest shade in the SEM images in the studied alloys 23 .Xu et al. 24  Cooling under a pressure of 6 GPa changed the coarse-grained Al 3 (Ni,Y) phase into branched dendrites 24 .The presence of thick, lamellar precipitates of the Al-Ni-Y phases was also observed in the studied alloys.Similar microstructures were also presented in ref. 25 for the multiphase Al 85 Ni 7 Fe 4 La 4 alloy in the form of an ingot.The α-Al phase, similar to the studied alloys, was identified as the darkest precipitates.In ref. 25 , the authors indicated the phase marked Al 9 Ni 1−x Fe x as oblong, oriented along one direction of the plate.In the case of the studied alloys, the largest number of reflections for the Al 9 Ni 1.3 Fe 0.7 phase was identified in the XRD patterns of the Al 79 Ni 11 Fe 5 Y 5 alloy.Based on the EDX maps, the Al 9 Ni 1.3 Fe 0.7 phase was marked in the SEM image as mediumgray precipitates.In contrast to the microstructure described in ref. 25 , an orientation along one direction was not observed for the Al 9 Ni 1.3 Fe 0.7 phase.4 shows the HRTEM images and selected area electron diffractions (SAED) pattern.The microscopic observations showed that the studied alloys were characterized by a homogeneous structure devoid of crystallites.Structures in the high-resolution mode were characterized by atomic disorder, referred to in the literature 26 as the "salt and pepper" effect.In addition, the presence of an amorphous structure for the Al 79 Ni 5 Fe 5 Y 11 and Al 79 Ni 11 Fe 5 Y 5 alloys was confirmed by the SAED results due to the broadened ring patterns.
The elemental distributions were collected for Al 79 Ni 5 Fe 5 Y 11 (Fig. 5) and Al 79 Ni 11 Fe 5 Y 5 (Fig. 6) alloys in ribbon form.The external morphology of the samples was also obtained in SE mode.The alloys were assigned as homogeneous single-phase structures with no segregation.It can be seen that the maps presented areas with different concentrations of Al, Ni, Fe, and Y elements according to the nominal chemical compositions of the samples.The homogeneous concentration of the elements also confirmed the amorphous structure of the tested ribbons.Previous works 27,28 have reported that an amorphous structure was obtained on the surface as a result of contact with the copper wheel during the melt-spinning process.The influence of material surface contact during cooling on the structure was described, i.e., for Ti-Ni-Cu alloys produced by the melt-spinning method.An amorphous zone (called the contact surface) and the crystalline zone (called the free surface) were visible on the cross-sectional SEM images of the studied ribbons 27 .
Figure 7 shows the neutron diffraction patterns of the alloys in the form of melt-spun ribbons.Broad diffraction peaks indicating the reflections of crystallites were observed for both alloys.The reflections for the α-Al and Al 8 Fe 4 Y phases were identified for the Al 79 Ni 5 Fe 5 Y 11 alloy, while reflections for the Al 8 Fe 4 Y phase were observed for the Al 79 Ni 11 Fe 5 Y 5 alloy.The penetration depth of neutrons in matter is much deeper compared with X-rays and electrons; therefore, according to ref. 29 , neutron radiation is useful for studying bulk materials.According to literature data 30,31 , the amorphous structure of metallic glasses should make them resistant to irradiation.Yang et al. 30 studied the structural responses of ZrCu metallic glasses under neutron irradiation and did not observe the formation of any crystalline phase, even though they confirmed its presence by synchrotron-based high-energy X-ray diffraction.However, in the same article 30 , the mechanisms of neutron irradiation that damaged the microstructure of amorphous alloys remained elusive.In this study, the melt-spun ribbons likely had a heterogeneous structure.
Mössbauer spectra with their adjustments obtained for the Al 79 Ni 5 Fe 5 Y 11 and Al 79 Ni 11 Fe 5 Y 5 alloys in the form of ribbons are shown in Fig. 8.These spectra were fitted with non-magnetic components (quadrupole doublets) 32 .The determined hyperfine parameters of these components are summarized in Table 1.The spectrum of the Al 79 Ni 11 Fe 5 Y 5 alloy contained two doublets, indicating the presence of two different local environments of iron atoms.The isomeric shifts (Is) of both these doublets were similar and in the range of 0.19-0.21mm/s, but these components differed significantly in their quadrupole splitting (Qs).The Qs range was 0.25-0.29 mm/s for the first doublet, and 0.54-0.56mm/s for the second.Taking into account the XRD results for these alloys, we can   23 .The component with higher values of quadrupole splitting will be associated with iron atoms having mainly aluminium and yttrium in their local environments, and the doublet with lower Qs values will be associated with iron atoms surrounded mainly by aluminium and nickel atoms.Yttrium atoms with a larger atomic radius than nickel atoms caused greater distortion of the local iron environment, hence higher values of quadrupole splitting.
To describe the thermal events under heating and cooling, the crystalline alloys (in the form of ingots) and amorphous ribbons were analyzed using DSC.As seen in Fig. 9, the DSC curve of the Al 79 Ni 5 Fe 5 Y 11 ingot showed three endothermic peaks at 637 °C, 890 °C and 982 °C during heating from room temperature to 1100 °C,   According to literature data 19,22,34 , the thermal event above 600 °C probably corresponded to the melting of the α-Al phase during heating and its crystallization during cooling.A similar course of the DSC curve as the Al 79 Ni 11 Fe 5 Y 5 ribbons was presented in ref. 35 for the Al 84.5 Ni 5.5 Y 10 alloy with an amorphous structure in the form of a high-pressure cast rod.In ref. 35 , three distinct, consecutive exothermic events and one endothermic event were recorded.Fu et al. 35 stated that the exothermic peaks  www.nature.com/scientificreports/corresponded to the crystallization of the amorphous structure, while the endothermic event was related to the glass transition.However, on the basis of ref. 4,36 most of Al-based metallic glasses do not show a clear T g glass-transition event because the onset of the T x primary crystallization peak almost coincides with the glass transition.Moreover, according to the authors of ref. 35 , the liquid phase was present in practically the entire volume of the alloy after the first endothermic peak.On the basis of the DSC curve in ref. 35 , the glass transition temperature (T g ), onset crystallization temperature (T x1 ), melting point (T m ), and liquidus temperature (T l ) were determined, respectively, as 207 °C, 244 °C, 617 °C, and 959 °C.Exothermic effects recorded for the Al 79 Ni 11 Fe 5 Y 5 alloy occurred at higher temperatures due to differences in the chemical composition of the amorphous phase.
In addition, two additional endothermic effects were observed in the DSC curve for the Al 79 shows the XRD patterns with Miller indices for the identified phases.The studied ingots possessed a multiphase crystalline structure.The following phases were identified for the Al 79 Ni 5 Fe 5 Y 11 alloy: Al 10 Fe 2 Y, Al 3 Y, Al 23 Ni 6 Y 4 , and α-Al.In the structure of the Al 79 Ni 11 Fe 5 Y 5 alloy, three phases were identified: Al 19 Ni 5 Y 3 , Al 9 Ni 1.3 Fe 0.7 , and α-Al.
, the phase crystallization sequence in the alloy with a similar chemical composition Al 87 Ni 9 Y 4 is as follows: α-Al, Al 3 Ni, and Al 19 Ni 5 Y 3 .The Al 23 Ni 6 Y 4 phase was identified in the Al 79 Ni 5 Fe 5 Y 11 alloy, while the presence of the Al 19 Ni 5 Y 3 phase was demonstrated for the Al 79 Ni 11 Fe 5 Y 5 alloy.Similarly to ref. 20 , the Al 3 Ni phase was not identified, which should be present, according to the Al-Ni-Y phase equilibrium diagram.On the other hand, the Al 3 Y phase was identified only for the Al 79 Ni 5 Fe 5 Y 11 alloy, which resulted from the higher atomic content of yttrium.Al-Fe phases were not found in the Al 79 Ni 11 Fe 5 Y 5 alloy, probably due to the depletion of iron in the alloy after crystallization of the Al 9 Ni 1.3 Fe 0.7 and Al 10 Fe 2 Y phases.The presence of a multiphase crystalline structure in the Al 79 Ni 5 Fe 5 Y 11 and Al 79 Ni 11 Fe 5 Y 5 ingots was confirmed by microstructure observations using SEM.The images of the microstructures in the backscattered electron (BSE) mode and the EDX element distribution maps are shown in Fig. 2. In the studied alloys, phases consisting of aluminium, nickel, and yttrium (Al 19 Ni 5 Y 3 and Al 23 Ni 6 Y 4 ) were present in the form of lamellar precipitates.The EDX maps confirmed the presence of the α-Al phase due to the presence of areas characteristic of aluminium (marked in red).This was confirmed by the presence of the α-Al phase, for which two high-intensity peaks were identified in the XRD patterns in studied ingots.
presented the microstructure of an Al-Ni-Y alloy produced using slow cooling and under pressure.Using both solidification methods, the Al 88 Ni 7 Y 5 alloy consisted of α-Al, Al 3 (Ni,Y) and Al(Ni,Y) phases.The slowly cooled alloy was characterized by a structure consisting of thick plates of the Al 3 (Ni,Y) phase and thin needles of the Al(Ni,Y) phase.

Figure 3
presents the XRD patterns of melt-spun Al 79 Ni 5 Fe 5 Y 11 and Al 79 Ni 11 Fe 5 Y 5 alloys, which indicates an amorphous structure because of the characteristic amorphous "halo" and the lack of crystalline reflections.However, the XRD pattern of Al 79 Ni 11 Fe 5 Y 5 was characterized by a broad peak that indicated a double-amorphous state.

Figure 1 .
Figure 1.X-ray diffraction patterns of Al 79 Ni 5 Fe 5 Y 11 (a) and Al 79 Ni 11 Fe 5 Y 5 (b) in the form of ingots.

Figure 2 .
Figure 2. SEM images of the microstructures of Al 79 Ni 5 Fe 5 Y 11 (a) and Al 79 Ni 11 Fe 5 Y 5 (b) alloys in the form of ingots in BSE mode with element distribution maps.

Figure 3 .
Figure 3. X-ray diffraction patterns of Al 79 Ni 11 Fe 5 Y 5 and Al 79 Ni 5 Fe 5 Y 11 in the form of ribbons. Figure

Figure 4 .
Figure 4. HRTEM images (a, c) and SAED patterns (b, d) of the Al 79 Ni 5 Fe 5 Y 11 and Al 79 Ni 11 Fe 5 Y 5 alloys in the form of melt-spun ribbons.

Figure 5 .
Figure 5. Microstructure of Al 79 Ni 5 Fe 5 Y 11 alloy in ribbon form with EDX element distribution maps.

Figure 6 .
Figure 6.Microstructure of Al 79 Ni 11 Fe 5 Y 5 alloy in ribbon form with EDX element distribution maps.

Figure 7 .
Figure 7. Neutron diffraction patterns of Al 79 Ni 5 Fe 5 Y 11 (a) and Al 79 Ni 11 Fe 5 Y 5 (b) alloys in the form of ribbons.

Figure 9 .
Figure 9. DSC heating (a) and cooling (b) curves of Al 79 Ni 5 Fe 5 Y 11 and Al 79 Ni 11 Fe 5 Y 5 alloys in the form of ingots.

Figure 10
shows the DSC curves recorded in the temperature range of 200-1000 °C at the rate of 10 °C/min during heating for Al 79 Ni 5 Fe 5 Y 11 and Al 79 Ni 11 Fe 5 Y 5 alloys in the form of ribbons.Figure 11 also shows the DSC curves for the same ribbons over a smaller temperature range (200-700 °C) and with a higher heating rate (20 °C/ min).In the DSC curves (Fig. 10), three exothermic events appeared during heating at 390 °C, 433 °C, and 499 °C for Al 79 Ni 11 Fe 5 Y 5 ribbon.Moreover, three endothermic events at 630 °C, 796 °C and 922 °C were also recorded.The DSC curve of the Al 79 Ni 5 Fe 5 Y 11 ribbon showed one clear exothermic peak recorded at 412 °C as well as endothermic event at 630 °C.An endothermic reaction with a low enthalpy was also recorded at 900 °C.The recorded baseline for the ribbon with a higher yttrium content was characterized by an unstable course, probably related to the movement of metallic liquid in the measuring crucible.Based on the DSC curves shown in Fig. 11, T x (onset crystallization temperature), T p (crystallization peak temperature), and T m (melting temperature) were determined.The Al 79 Ni 11 Fe 5 Y 5 alloy was characterized by a lower temperature at the beginning of crystallization of the amorphous phase (T x = 390 °C) compared with Al 79 Ni 5 Fe 5 Y 11 alloy (T x = 408 °C).Similarly to Fig. 10, two additional exothermic events were observed for the Al 79 Ni 11 Fe 5 Y 5 alloy with crystallization temperatures of 434 °C and 507 °C.The Al 79 Ni 11 Fe 5 Y 5 (T m = 632 °C) and Al 79 Ni 5 Fe 5 Y 11 (T m = 631 °C) alloys were characterized by similar melting onset temperatures determined from the recorded endothermic event.

Figure 10 .
Figure 10.DSC heating curves of Al 79 Ni 5 Fe 5 Y 11 and Al 79 Ni 11 Fe 5 Y 5 alloys in the form of melt-spun ribbons.

Figure 11 .
Figure 11.DSC heating curves of Al 79 Ni 5 Fe 5 Y 11 (a) and Al 79 Ni 11 Fe 5 Y 5 (b) alloys in the form of melt-spun ribbons.
Ni 11 Fe 5 Y 5 alloy.The crystallization mechanisms of Al 85 Ni 10 Y 5 and Al 85 Ni 5 Fe 5 Y 5 alloys are described in ref. 34 based on the XRD patterns obtained in situ at variable temperatures and the results of differential thermal analysis (DTA).Similarly to the Al 79 Ni 5 Fe 5 Y 11 and Al 79 Ni 11 Fe 5 Y 5 alloys, exothermic effects related to the crystallization of the amorphous phase were recorded on the DTA curves.On the basis of the diffractograms, it was estimated that in the Al 85 Ni 10 Y 5 alloy, after the formation of the α-Al phase, the Al 19 Ni 5 Y 3 phase crystallized at 340 °C.The temperature of 400 °C was associated with the crystallization of the Al 15 Fe 9 Y 2 phase in both the Al 85 Ni 10 Y 5 and Al 85 Ni 5 Fe 5 Y 5 alloys.According to ref. 34 , the last stage was the crystallization of the AlNiY and Fe 0.7 Ni 1.3 Al 9 phases.Conclusions The ingots possessed a multiphase crystalline structures.Melt-spinning method was used to obtain supercooled alloys in the form of ribbons.The amorphous structure of the ribbons was confirmed by XRD, SEM, and TEM, however the results of neutron diffraction studies indicate that the melt-spun alloys exhibited amorphous matrix structure with the presence of crystalline phases.The diffraction pattern of the Al 79 Ni 5 Fe 5 Y 11 ribbon indicated the presence of an amorphous structure, while the Al 79 Ni 11 Fe 5 Y 5 alloy was characterized by a double-broadened peak that indicated the presence of two types of atomic disorder.Furthermore, exothermic events in the DSC curves indicated the occurrence of crystallization from the amorphous phase at 408 °C for the Al 79 Ni 5 Fe 5 Y 11 alloy and at 387 °C for the Al 79 Ni 11 Fe 5 Y 5 alloy.

Table 1 .
The Mössbauer hyperfine parameters of the investigated samples.Is -isomer shift, Qs -quadrupole splitting, FWHM -full width at half maximum, A -relative area from the spectra, * -parameters related to p(Qs) of Al 79 Ni 5 Fe 5 Y 11 and Al 79 Ni 11 Fe 5 Y 5 alloys in the form of ribbons.